Most commercially-available hydrogel contact lenses are produced according to a conventional cast molding technique involving use of disposable plastic molds and a mixture of vinylic monomers and crosslinking agents. There are several disadvantages with the conventional cast-molding technique. For example, a traditional cast-molding manufacturing process often includes lens extraction in which unpolymerized monomers must be removed from the lenses by using an organic solvent. Use of organic solvents can be costly and is not environmentally friendly. In addition, disposable plastic molds inherently have unavoidable dimensional variations, because, during injection-molding of plastic molds, fluctuations in the dimensions of molds can occur as a result of fluctuations in the production process (temperatures, pressures, material properties), and also because the resultant molds may undergo non-uniformly shrinking after the injection molding. These dimensional changes in the mold may lead to fluctuations in the parameters of contact lenses to be produced (peak refractive index, diameter, basic curve, central thickness etc.) and to a low fidelity in duplicating complex lens design.
The above described disadvantages encountered in a conventional cast-molding technique can be overcome by using the so-called Lightstream Technology™ (CIBA Vision), which involves (1) a lens-forming composition being substantially free of monomers and comprising a substantially-purified, water-soluble prepolymer with ethylenically-unsaturated groups, (2) reusable molds produced in high precision, and (3) curing under a spatial limitation of actinic radiation (e.g., UV), as described in U.S. Pat. Nos. 5,508,317, 5,583,163, 5,789,464, 5,849,810, 6,800,225, and 8,088,313. Lenses produced according to the Lightstream Technology™ can have high consistency and high fidelity to the original lens design, because of use of reusable, high precision molds. In addition, contact lenses with high quality can be produced at relatively lower cost due to the short curing time, a high production yield, and free of lens extraction and in an environmentally friendly manner because of use of water as solvent for preparing lens formulations. However, the Lightstream Technology™ has not been applied to make contact lenses capable of absorbing ultra-violet (UV) lights (between 280 nm and 380 nm) and optionally high-energy violet lights (HEVL) (between 380 nm and 440 nm), largely because commercially-available polymerizable UV-absorbing vinylic monomers and those disclosed in U.S. Pat. Nos. 4,612,358, 4,528,311, 4,716,234, 7,803,359, 8,153,703, 8,232,326, and 8,585,938 (herein incorporated by reference in their entireties) are not water-soluble and cannot be used in the production of contact lenses from a water-based lens formulation.
Therefore, there are still needs for a new water-soluble UV-absorbing vinylic monomer or a new water-soluble UV/HEVL-absorbing vinylic monomer for making UV-absorbing or UV/HEVL-absorbing contact lenses from a water-based lens formulation.